Grammar rules exist to help us communicate clear and meaningful messages. Many grammatical rules are sacred and should never be violated, such as misusing homonyms and idioms, or choosing the wrong word (e.g., “there” instead of “their”). Such mistakes make us sound incompetent (when we’re not) and damage credibility. Writing for online is different than writing for print:

Web users are often action oriented, "leaning forward" in the hunt for answers to their current question, rather than leaning back to absorb a good book.

Web content is distributed among multiple locations — often on separate websites — whereas print content is usually delivered as a single object with no separate navigation other than turning the page.

Interactive users read very few words on most web pages, because they're impatient and already have their mouse-finger itching to move to the next page.

People can be confused or misled when a search lands them on a web page divorced from the context provided if they had read the rest of the site. Elaborate writing styles take too long to set newly-arrived users straight.

Some grammar rules are worth breaking if you have good reason. But before I give you my list of top rules to break, it’s important to emphasize that I’m not advocating that writers break rules with abandon or become sloppy. You must first know the rules before you can break them effectively.

The rules that you can violate depend on the context, the target audience, and the brand or tone of voice. For example, the tone applied to professional publications is usually more formal than the tone of blog posts from the same company. Formal tone usually requires adhering to traditional writing conventions more closely, whereas conversational tone allows for greater flexibility.

With that said, the following list applies to almost any website. With balanced usage, breaking these rules can result in better scannability and comprehension.

Break Rule #1: Never use sentence fragments

Sentence fragments are incomplete sentences, usually missing a subject or verb. Complete sentences are important because they express a complete idea. While it’s advisable to write complete sentences, when applied sparingly, fragments can add impact. Help readers feel what you feel.

For web readers,snippets are a plus because they allow users to scan without having to read the full body copy. When sentence fragments are done correctly, readers can borrow words from the previous sentence to make the fragment whole. Context fills in the gaps.

Lift.do: While these sentences are short, they don’t contain enough information to communicate what this product does. Beware: Short is not always better if critical information is missing or context is not established.

Break Rule #2: Spell out small numbers

A common writing rule for numbers is to spell out whole numbers less than 10; reserve the numeric format for numbers 10 or greater.

Compare the two following phrases. Version A is grammatically correct, but more difficult to process than Version B. Spelling out the numbers makes them harder to spot and remember than writing them numerically.

Version A: Our solar system consists of eight planets. There are four planets that have rings around them.

Version B: Our solar system consists of 8 planets. There are 4 planets that have rings around them.

Version B makes it easier for people to scan and identify the numbers. (Particularly if they were trying to find out something like "what percentage of planets have rings," which is a typical reason a search might have led the user to that page in the first place.) When reading online, users scan the page for clues that may answer their question. If the answer that they seek is a number, then numeric format usually gets more attention than the written version. The numeric format also makes it easier for people to compare numbers because they stand out. For example, if readers must figure out the percentage of planets that have rings, Version B would make the process easier.

Break Rule #3: Paragraphs should contain 3–5 sentences

Traditionally, instructors have encouraged young students to write paragraphs with at least 3-5 sentences. Sometimes the point that you need to make will require several sentences and sometimes it won’t. If you can get the job done in one sentence, do it. One-sentence paragraphs can provide impact and draw attention to key points that might otherwise be buried.

This technique facilitates scanning because it gives readers a break. It’s much easier to read small paragraphs than large blocky ones.

Nytimes.com: Small digestible paragraphs like these feel inviting and facilitate scanning.

Conclusion

Ignoring all writing rules is not going impress anyone. However, some rules are worth breaking to facilitate scanning and heighten comprehension and mood. The overarching tenet: Break grammar rules for clarity and speed. In moderation. Learn more about web writing techniques at Usability Week.